Tractor-trailers that transport cargo on roads and highways can have varying gross weights depending on various factors, especially the nature and amount of cargo. Knowledge of the gross weight of a tractor-trailer combination can be important for any of various reasons.
Gross weight of a tractor-trailer combination can of course be measured by driving the combination onto a suitable scale. However, such a scale is not necessarily always available when there is a need to measure weight. Moreover, such a measurement will not give the weight of the trailer alone unless the weight of the tractor is known, in which case tractor weight can simply be subtracted from the weight of the combination to yield the trailer weight.
The gross weight of a tractor typically changes only a relatively small amount depending in large part on the extent to which its fuel tanks are filled. That is typically not the case with a trailer where gross trailer weight is significantly greater when the trailer is fully loaded than when empty. Furthermore, weighing a trailer by itself can be inconvenient because of the constructional nature of the trailer where wheels at the rear bear only some of the weight while the remainder is borne either by the tractor when the trailer is connected to it or by a landing gear that is deployed to support the front of the trailer when disconnected from a tractor.
Known methods for on-board measurement of the weight of a tractor-trailer involve the use of sensors associated with the suspension system of each. Sensors associated with the tractor suspension system can furnish data for indicating the front and rear axle weights, which will include the effect of the portion of the trailer weight being borne by the tractor through the fifth wheel. Because at least one sensor is associated with the rear wheel suspension of the trailer, data from such a sensor or sensors must be electrically transmitted in one way or another from the trailer to the tractor in order for a complete estimate of tractor-trailer weight to be obtained.